--- title: "SMS 101: the text message every phone can receive" summary: "What SMS is, how a business text travels to a phone, what it costs, the registration and consent rules by region, and when plain text is still the right choice." canonical: https://cpaas.co/en/learn/sms-101 kind: explainer depth: foundation origin: original published: 2026-10-13T16:26:18.899Z updated: 2026-10-14T16:26:19.702Z topics: ["SMS", "Messaging", "A2P", "Fundamentals"] language: en --- # SMS 101: the text message every phone can receive ## At a glance SMS (Short Message Service) is the plain text message built into every mobile phone network. A business sends it through a provider, the recipient's mobile operator delivers it, and it lands in the same inbox as messages from family and friends. There is no app to install and no account to create. ```diagram:compare | SMS | What it means for you What it is | Plain text, up to 160 basic characters per segment | Short, simple messages; longer ones are split and billed per part Who runs it | Mobile operators, under national regulators | Rules and prices change by country, sometimes by network Reach | Any mobile phone with a number | The widest reach of any messaging channel Who may start | Either side; business marketing needs consent | Permission rules differ by country How it is priced | Per segment, by destination country | Long or non-Latin messages cost more Best for | Codes, reminders, alerts, fallback | Time-sensitive messages that must reach everyone Avoid for | Rich content, long chats, sensitive data | No images, no buttons, no proof of reading > As of October 2026. ``` Reach is the reason SMS survives every new channel. The International Telecommunication Union (ITU) estimates that 82% of people aged 10 and over owned a mobile phone in 2025[^1], and the GSMA, the mobile operators' association, counts about 5.8 billion unique mobile subscribers, around 70% of the world's population[^2]. Every one of those phones can receive a text. ## How it works A business text is an [A2P](/en/learn/glossary#a2p) message: application to person. Your software writes it; a person reads it. ```diagram:path # The path of one business text Your system | Writes the message and calls the provider's API | The message and the number Provider | Checks it, picks a route to the right operator | The message, in the operator's protocol Operator's message centre | Stores it until the phone can take it | The message, over the radio network Handset | Shows it in the messaging app | A delivery receipt Your system | Records delivered or failed | ``` 1. **Your system** sends the text and the phone number to a provider through an API. 2. **The provider** (often called an aggregator) has connections to [mobile operators](/en/learn/glossary#carrier), usually over a protocol called [SMPP](/en/learn/glossary#smpp). It checks the number, picks a route and passes the message on. 3. **The operator's message centre** stores the message and forwards it when the phone is reachable. SMS is a store-and-forward service defined in the 3GPP mobile standards[^3], which is why a text sent to a switched-off phone can still arrive hours later. 4. **The handset** shows it. The network sends back a [delivery receipt](/en/learn/glossary#delivery-receipt): proof the phone received it, not proof anyone read it. ### Who the message comes from The "from" line is called the [sender ID](/en/learn/glossary#sender-id). There are four kinds: an ordinary [long code](/en/learn/glossary#long-code) (a normal phone number), a [short code](/en/learn/glossary#short-code) (five or six digits leased for high volume), a [toll-free number](/en/learn/glossary#toll-free-number) in North America, and an [alphanumeric sender ID](/en/learn/glossary#alphanumeric-sender-id) such as your brand name. Brand names cannot receive replies, and some countries do not allow them at all. ### Segments, and why Arabic costs more One SMS segment carries 140 bytes. Using the basic GSM alphabet, that holds 160 characters. If the message contains even one character outside that alphabet, such as an Arabic, Hindi or Chinese letter or most emoji, the whole message switches to a 16-bit encoding called UCS-2 and a segment holds only 70 characters[^4]. A few symbols from the alphabet's extension table, such as the euro sign, take two places each[^4]. Longer messages are split into parts, each carrying a small header that tells the phone how to put them back together[^3], so each part holds a little less. You pay for every part. ```diagram:bars # Characters in one SMS segment Basic GSM alphabet | 160 | Latin letters, digits, common symbols Anything outside it | 70 | Arabic, Hindi, Chinese, most emoji > From 3GPP TS 23.038: the same 140 bytes, two encodings. ``` ## A short history On 3 December 1992, engineer Neil Papworth sent the words "Merry Christmas" over the Vodafone network in the UK to a handset weighing 2.1 kg, held by Vodafone director Richard Jarvis[^5]. SMS had been designed as a side feature of GSM, the European digital mobile standard; its alphabet and 160-character limit are still written in the same family of specifications today[^4]. Texting became the way people talked, and businesses followed. Because a text cost the sender so little, unwanted marketing arrived with it. In 2002 the European Union's ePrivacy Directive required prior consent for direct marketing by automated calls, fax and electronic mail, a definition that covers texts[^14]. The last few years have been about trust. Countries started requiring businesses to register who they are before sending: Saudi Arabia stopped texts from unregistered sender names after September 2022[^22]; in the US, carriers deliver business traffic on ordinary numbers only from registered brands and campaigns[^6]; India added link whitelisting in October 2024 and rejected texts on undeclared routes from December 2024[^18][^19]. In 2026 the UK regulator Ofcom set new rules for sender IDs[^17] and the US Federal Communications Commission (FCC) changed how people may withdraw consent[^11]. ```diagram:timeline # From "Merry Christmas" to registered senders 3 December 1992 | First SMS | "Merry Christmas" over the Vodafone network 2002 | EU ePrivacy Directive | Prior consent for marketing by electronic mail, including texts September 2022 | Saudi sender-name deadline | Texts from unregistered names stopped March 2023 | First US text-blocking rule | Operators block texts from numbers that should never send them October 2024 | India whitelists links | Only registered links may appear in business texts December 2024 | India enforces traceable routes | Texts on undeclared routes rejected July 2026 | Ofcom sender-ID rules | Operators must check business sender names September 2026 | FCC opt-out change | Senders may name one way to withdraw consent ``` ## Where it is used SMS is used wherever there are phones, which is almost everywhere. The ITU's 2025 figures show the shape of that reach: ownership is above 95% in high-income economies and 82% worldwide, but 66% in Africa and 53% in low-income economies[^1]. Where a phone exists, it can receive a text, even when it has no data plan. ```diagram:bars # Share of people aged 10+ who own a mobile phone, 2025 High-income economies | 95% | Above this level World | 82% | Africa | 66% | Low-income economies | 53% | > ITU Facts and Figures 2025. ``` What differs between regions is less the reach than the rules and the habits around it: - **Americas.** In the US and Canada, businesses text from short codes, toll-free numbers and registered ordinary numbers (called [10DLC](/en/learn/glossary#10dlc) in the US); brand names are not used as senders in the US. Industry guidelines from CTIA, the US wireless association, set expectations on consent and opt-out[^9]. - **Europe.** Brand-name senders are common. Consent law (the ePrivacy rules and, in the UK, PECR) governs marketing[^14][^15], and regulators are now targeting sender-ID abuse[^17]. - **Middle East and Africa.** The Gulf states require sender names to be registered, with promotional messages marked "AD"[^21][^22]. Nigeria began licensing international A2P messaging aggregators in 2025[^23]. In much of Africa, SMS reaches people chat apps cannot, because ownership runs ahead of internet use[^1]. - **Asia-Pacific.** India runs one of the strictest systems: every business sender, message template and link is registered on operators' ledgers before sending[^18][^20]. ## What businesses use it for - **[One-time codes](/en/ecosystem/use-cases/otp).** The largest use. A code by text proves someone holds the phone number right now. NIST, the US standards institute, treats codes sent over the phone network as a "restricted" option because numbers can be hijacked[^24], so banks pair them with checks such as a [SIM swap check](/en/learn/glossary#sim-swap-check), which operators increasingly offer through standard network APIs[^25]. - **[Notifications](/en/ecosystem/use-cases/notifications).** Delivery updates, payment confirmations, service alerts. - **[Booking](/en/ecosystem/use-cases/booking) and [no-shows](/en/ecosystem/use-cases/no-shows).** Appointment reminders with "reply 1 to confirm". - **[Marketing](/en/ecosystem/use-cases/marketing).** Offers and announcements, only with consent and only where rules allow. - **[Support](/en/ecosystem/use-cases/support).** Two-way conversations, if your sender can receive replies. ## What it costs SMS is priced **per segment**, at a rate set by the destination country and sometimes by the operator. Three things move the bill: - **Length and script.** A 200-character Arabic message is three segments, an English one of the same length two[^4]. - **The sender type.** Short codes, toll-free numbers and brand names carry their own setup, monthly or registration fees in many countries. - **Registration.** In the US, The Campaign Registry's fee guide (13 August 2026) lists $4.50 to register a brand and $41.50 for a standard third-party vet[^7]. T-Mobile notes that messaging providers may also charge fees for sanctioned business traffic[^6]. Toll-free numbers must be verified before they can text; unverified ones have been blocked since 31 January 2024[^8]. ```diagram:checklist # What goes into an SMS bill Segments, not messages | Count your real messages, in your real languages The destination's rate | Set per country, sometimes per operator Sender fees | Short codes, toll-free and brand names may carry their own Registration and vetting | One-off and recurring, where the market requires it [!] A single average price per message | It hides segments, countries and fees ``` There is no single public price list for SMS; each provider publishes its own per country. Compare quotes on the same sample of your real messages, in the countries you actually send to. ## Rules and regulation This is a summary, not legal advice. Two questions apply everywhere: are you registered to send, and do you have permission? ### Americas In the US, business texts on ordinary numbers must be registered as a brand and a campaign before carriers approve them for delivery[^6]. CTIA's guidelines ask senders to get consent, honour opt-out words such as STOP, END or UNSUBSCRIBE, and never use rented or bought lists[^9]. The FCC treats a reply such as "stop", "quit", "end", "revoke", "opt out", "cancel" or "unsubscribe" as a valid way to withdraw consent[^10]; in September 2026 it allowed senders to name an exclusive opt-out method, provided they disclose it clearly in every message[^11]. Operators must also block texts from numbers that should never send them, such as invalid or unallocated numbers[^13], and, under rules adopted in December 2023, must block a number's texts once the FCC flags them as suspected illegal; the same rules confirmed that Do-Not-Call protections apply to texts[^12]. ### Europe Under the EU ePrivacy Directive, marketing by electronic mail, which includes texts, needs prior consent, with a narrow exception for a business's own existing customers who were given an easy way to refuse[^14]. The UK's equivalent, PECR, works the same way: specific consent, or the "soft opt-in" for your own similar products[^15]. Since the Data (Use and Access) Act 2025 came into force, the ICO can fine PECR breaches up to £17.5 million or 4% of global turnover[^16]. Ofcom's 2026 rules require UK operators to check each business's sender ID against what they know about the business, and to block scam messages in transit[^17]. ### Middle East and Africa In the UAE, the regulator TDRA requires promotional texts to carry a sender name starting "AD-", explicit consent, sending only between 7am and 9pm, and a free opt-out; people can block promotional senders by texting 7726[^21]. Saudi Arabia's regulator CST requires bulk SMS sender names to be registered in a shared system; texts from unregistered names were stopped after 30 September 2022[^22]. Nigeria's regulator licenses international A2P messaging aggregators[^23]. ### Asia-Pacific India's regulator TRAI requires every business sender, template and header to be registered on operators' [DLT](/en/learn/glossary#dlt) platforms. Since 1 October 2024 links in business texts must be whitelisted[^18], and since 11 December 2024 texts on undeclared routes are rejected[^19]. A 2025 amendment defines transactional messages narrowly: those sent within thirty minutes of a transaction the customer started[^20]. ```diagram:compare | Register before sending | Marketing consent United States | Brand and campaign (10DLC), or verified toll-free | Expected; opt-out words must work UK and EU | Not a central registry; operators check senders in the UK | Prior consent or soft opt-in UAE and Saudi Arabia | Sender names registered; promotions marked AD | Explicit consent in the UAE India | Sender, templates and links on DLT | Preferences recorded on the same system ``` ## Limits and pitfalls - **Plain text only.** No images, buttons or brand logo. Anything richer needs a link, and links are what filters inspect most closely. - **No proof of reading.** A delivery receipt says the phone received the message. Measure what people do, not what was delivered; see [delivery rate is not a result](/en/learn/delivery-rate-is-not-a-result). - **Weak sender identity.** A sender name can be imitated, which is why scam texts so often look like banks and parcel firms; regulators are only now making operators check them[^17]. - **Brand names are one-way.** A customer cannot reply "1" to an alphanumeric sender. - **Segment surprises.** One emoji in a template can double its cost[^4]. - **Fraud on sign-up forms.** Bots can trigger codes to expensive numbers so fraudsters share the revenue. Rate-limit code requests and watch destination countries you do not serve. - **Opt-outs that do not work.** STOP must work on every sender you use[^9][^10]. ## Strengths and weaknesses ```diagram:compare | Strengths | Weaknesses Reach | Almost any mobile phone, no app or data | Coverage of rules varies by country Speed | Arrives in seconds on most routes | Bulk sends queue; registration limits throughput Trust | Lands beside personal messages | Sender names can be spoofed Content | Simple and universal | Plain text, no buttons, no read receipts Cost | Predictable per segment | Rises with length, script and destination ``` ## What comes next - **The UK.** Ofcom's new rules take effect for person-to-person messaging on 18 January 2027 and for business messaging on 15 July 2027; Ofcom decided against a mandatory sender-ID registry[^17]. - **The US.** Alongside its September 2026 order, the FCC asked whether to require a single "revoke all" option and whether to shorten the ten business days senders have to honour an opt-out[^11]. - **Network APIs.** Operators increasingly expose checks such as SIM swap through the GSMA's Open Gateway programme, which makes text codes safer to rely on[^25]. - **RCS.** The rich successor to SMS uses the same phone numbers and falls back to SMS where it is not available; see [RCS 101](/en/learn/rcs-101). ## When to choose it ```diagram:decision # Is SMS the right channel for this message? Must it reach people who may not have any particular app? | SMS, or SMS as the fallback | Is it short and time-sensitive, like a code or a reminder? | SMS works well | Does it need images, buttons or a long back-and-forth? | Use a richer channel, with SMS as fallback | SMS works, kept short ``` Choose SMS when reach matters more than richness: codes, reminders, alerts and the fallback for every other channel. Choose something richer, such as [RCS](/en/learn/rcs-101) or [WhatsApp](/en/learn/whatsapp-101), when the message needs pictures, buttons or a conversation, and keep SMS behind it. See the [SMS channel page](/en/ecosystem/channels/sms), compare channels message by message in [choosing a channel per message](/en/learn/choosing-a-channel-per-message), and weigh every channel by need, place and audience in [which channel for which need](/en/learn/which-channel-for-what). ## Sources [^1]: [Facts and Figures 2025: Mobile phone ownership](https://www.itu.int/itu-d/reports/statistics/2025/10/15/ff25-mobile-phone-ownership/) — International Telecommunication Union (ITU), 2025 [^2]: [The Mobile Economy 2026](https://www.gsma.com/mobileeconomy/) — GSMA, March 2026 [^3]: [ETSI TS 123 040 (3GPP TS 23.040): Technical realization of the Short Message Service (SMS), V12.2.0](https://www.etsi.org/deliver/etsi_ts/123000_123099/123040/12.02.00_60/ts_123040v120200p.pdf) — ETSI / 3GPP, October 2014 [^4]: [ETSI TS 123 038 (3GPP TS 23.038): Alphabets and language-specific information, V10.0.0](https://www.etsi.org/deliver/etsi_ts/123000_123099/123038/10.00.00_60/ts_123038v100000p.pdf) — ETSI / 3GPP, March 2011 [^5]: ['Merry Christmas': The 30th anniversary of the first text message](https://www.vodafone.co.uk/newscentre/features/merry-christmas-the-30th-anniversary-of-the-first-text-message/) — Vodafone UK News Centre, December 2022 [^6]: [Consumer versus Non-Consumer Text Messaging](https://www.t-mobile.com/support/plans-features/consumer-versus-non-consumer-text-messaging) — T-Mobile, accessed 2026-10 [^7]: [TCR Fees and Pricing: General Guide](https://www.campaignregistry.com/Assets/TCR%20Fees%20and%20Pricing.pdf) — The Campaign Registry, 13 August 2026 [^8]: [Toll-free verification and blocking of unverified toll-free numbers](https://support.twilio.com/hc/en-us/articles/5377174717595) — Twilio Support, accessed 2026-10 [^9]: [Messaging Principles and Best Practices](https://api.ctia.org/wp-content/uploads/2023/05/230523-CTIA-Messaging-Principles-and-Best-Practices-FINAL.pdf) — CTIA, May 2023 [^10]: [TCPA Rules Revoking Consent for Unwanted Robocalls/Robotexts](https://www.fcc.gov/document/tcpa-rules-revoking-consent-unwanted-robocallsrobotexts) — Federal Communications Commission (FCC), 2024 [^11]: [Report and Order FCC 26-67 (revocation of consent)](https://docs.fcc.gov/public/attachments/FCC-26-67A1.pdf) — Federal Communications Commission (FCC), 30 September 2026 [^12]: [Fact sheet: Combatting Illegal Text Messages](https://docs.fcc.gov/public/attachments/DOC-398661A1.pdf) — Federal Communications Commission (FCC), 22 November 2023 [^13]: [Report and Order FCC 23-21 (targeting and eliminating unlawful text messages)](https://docs.fcc.gov/public/attachments/FCC-23-21A1.pdf) — Federal Communications Commission (FCC), March 2023 [^14]: [Directive 2002/58/EC on privacy and electronic communications](https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32002L0058) — EUR-Lex, 12 July 2002 [^15]: [Guide to PECR: Electronic mail marketing](https://ico.org.uk/for-organisations/direct-marketing-and-privacy-and-electronic-communications/guide-to-pecr/electronic-and-telephone-marketing/electronic-mail-marketing/) — Information Commissioner's Office (ICO), accessed 2026-10 [^16]: [Statement on the commencement of the Data (Use and Access) Act (DUAA)](https://ico.org.uk/about-the-ico/media-centre/news-and-blogs/2026/02/statement-on-the-commencement-of-the-data-use-and-access-act-duaa/) — Information Commissioner's Office (ICO), February 2026 [^17]: [New rules to protect people and businesses against mobile messaging scams](https://www.ofcom.org.uk/phones-and-broadband/scam-calls-and-messages/new-rules-to-protect-people-and--businesses-against-mobile-messaging-scams) — Ofcom, 15 July 2026 [^18]: [TRAI mandates whitelisted URLs, APKs or OTT links for SMS traffic](https://www.pib.gov.in/PressReleaseIframePage.aspx?PRID=2058943®=48&lang=2) — Press Information Bureau, Government of India, 2024 [^19]: [TRAI achieves key milestone in ensuring SMS traceability for secure messaging](https://www.pib.gov.in/PressReleasePage.aspx?PRID=2086103) — Press Information Bureau, Government of India, December 2024 [^20]: [Telecom Commercial Communications Customer Preference (Second Amendment) Regulations, 2025](https://www.trai.gov.in/sites/default/files/2025-02/Regulation_12022025.pdf) — Telecom Regulatory Authority of India (TRAI), 12 February 2025 [^21]: [FAQs (promotional SMS, AD sender names and blocking)](https://tdra.gov.ae/en/FAQs) — Telecommunications and Digital Government Regulatory Authority (TDRA), UAE, accessed 2026-10 [^22]: [Final deadline extended to September 30, 2022 for entities benefiting from bulk SMS service to register their sender names](https://www.cst.gov.sa/en/media-center/news/CITC-Extension-of-the-Final-Deadline-for-Entities-Benefiting-from-the-Bulk-SMS-Service-to-Register-T) — Communications, Space and Technology Commission (CST), Saudi Arabia, 2022 [^23]: [Commencement of Licensing for the Provision of International A2P Messaging Aggregator Services](https://ncc.gov.ng/media-center/public-notices/commencement-licensing-provision-international-a2p-messaging-aggregator) — Nigerian Communications Commission, July 2025 [^24]: [NIST SP 800-63B-4: Digital Identity Guidelines, Authentication and Authenticator Management](https://csrc.nist.gov/pubs/sp/800/63/b/4/final) — National Institute of Standards and Technology (NIST), July 2025 [^25]: [GSMA Open Gateway](https://www.gsma.com/solutions-and-impact/gsma-open-gateway/) — GSMA, accessed 2026-10 --- Published by the company behind five products in this category. 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